The spatio-temporal dynamics of non-linear systems includes many examples of chaotic behavior interspersed with regular rhythmic activity. A simple system of this type is a pair of coupled oscillators in which one oscillator, itself driven by an external source, excites the second oscillator which, in turn, attempts to inhibit the first oscillator. The competitive interaction can generate a rhythmic behavior which, at one extreme, is a variable-rate train of sharp spike-like pulses and, at the other extreme, is a quasi steady-state balance that may be used for amplification of the original input signal emitted by the external source. The two extremes of the rhythmic behavior are reached by varying the temporal response and the nonlinearity of response in the two coupled oscillators.
An example of a system for generating a series of pulses is a biological neuron which may be called an integrate-and-fire pulse generator. The neuron is usually modeled as a leaky capacitor which shorts out when its voltage reaches a critical fixed threshold, then, after the burst of current (i.e. the pulse), self-repairs the short and begins to recharge. The self-repair effect is also seen in an oil-filled capacitor. The time period between pulses depends on the strength of the externally-applied charging input. The integrate-and-fire mechanism has been implemented in many electronic designs.
Optical non-linear systems are more difficult to fabricate because of two fundamental facts. First, light intensity is a positive-definite physical quantity. Unlike electronic voltage which can be either positive or negative, light intensity can only be positive or zero. Second, photons can be created and destroyed at will in optical systems whereas electrons are conserved in electronic systems. The nonlinear optical effects in materials are primarily due to the dependence of the electrical susceptibility on the electric field of the incident optical wave. For instance, zeroth order gives birefringence, first order gives photoelectrons and third order exhibits photorefractive effects.
Hence, prior art methods of generating pulses of light required the use of a hybrid system that combined some electronics and some optics.